Reference is hereby made to copending U.S. patent application Ser. No. 513,216 filed Oct. 9, 1974 by Peter B. Olmsted for a Flow Shut Off Valve.
Shipboard fluid control systems are subjected to a severe corrosive environment. Flow shut off valves used as protective devices on board offshore drill ships are particularly subject to the adverse environment and must be operable under sudden emergency conditions. Such a valve is disclosed in the application referred to above and includes means to exercise the valve under normal operating conditions thereby assuring operability of the valve under emergency conditions. The combined biasing and restraining means utilized to reciprocate the spool in normal operation causes internal resistance to the flow of fluid as a result of transient interruptions to flow as the spool cycles through the neutral position. The disclosures below comprise improvements to such exerciseable flow shut off valves resulting in substantially lower internal fluid resistance and smoother cyclic movement of the spool.